<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="lib/vue.js"></script>
</head>
<body>
    <div id="app"></div>
</body>
<script>
    let data ={
        num:1
    };
    const vm = new Vue({
        el:"#app",
        data,
        methods:{
            changeNum(v){
                this.num = v;
            }
        }
    });
    console.log(vm.$data === data);// true
    console.log(vm.num);// 1
    vm.changeNum(100);
    console.log(vm.num);// 100
    console.log(vm.$data.num);// 100
    console.log(111,vm.$el);
</script>
</html>